1. Field of the Invention
The present invention relates generally to electronic memory cells and switches. More particularly, the present invention involves three-terminal electronic memory and switching devices that utilize two organic memory cells or switching elements that exhibit electrical bistable behavior.
2. Description of Related Art
The publications and other reference materials referred to herein to describe the background of the invention and to provide additional details regarding its practice are hereby incorporated by reference. For convenience, the reference materials are numerically referenced and identified in the appended bibliography.
Devices with electrical bistability have been widely studied because they can be used as switches and memory elements, which are important for digital electrical instruments since they have two states of different conductivity. The reversible resistance switching process that occurs in inorganic thin films has engendered strong interest and much work has been done in this field. Recently, organic electrical switching and memory devices have attracted more attention because of the distinct advantages of organic materials, such as light weight, mechanical flexibility, etc. (1-11).
Organic bistable devices (OBD) and their electrical switching and memory effect have previously been reported (5-8). These devices include five thin films that form an organic/metal-nanocluster/organic triple layer that is sandwiched between two electrodes. When the voltage on the device is larger than a critical voltage, the device switches from a high impedance state (OFF state) to a low impedance state (ON state) and remains in the ON state until a negative voltage is applied. Recently, it was found that the metal-nanocluster layer can be formed by co-evaporation of metal and organic materials, instead of simply depositing the metal at slow deposition rate (8). We found that the devices fabricated in this way are highly reproducible. For convenience, in this specification we sometimes refer to the (middle) mixed layer as the metal-nanocluster layer.
Most memory devices based on conductance change are detected by measuring the device current. From application point of view, the memory cell should be as small as possible, such as in the micrometer or sub-micrometer scale, in order to achieve a high density of data storage. In this case, the current through the memory cell may be too small to be distinguished conveniently to determine whether the device is in ON state or OFF state. This issue may be overcome by increasing the ON state current of the device.